How straw return approaches affect runoff and sediment in croplands of different degradation degrees in the black soil region of China

Different straw return approaches have dissimilar soil disturbance and straw mixing extents, thus make distinct effects on rainfall-runoff-erosion processes. The variations in soil properties triggered by land degradation likely affect the fitness of straw return approach on mitigating soil and water loss. Quantitively assessing the suitability of straw return approaches for croplands with different degradation degrees and illustrating the involved impact mechanism are desirable. In this study, twelve erosive rainfall events were monitored during a soybean growth season in 2023 in the black soil region of Northeast China. Sixteen runoff plots were established under straw removal (CK), straw return by rotary tillage (SR), deep plowing (SP) and strip mulching (SM) treatments in croplands with four degradation degrees, i.e., non (ND), light (LD), moderate (MD) and strong (SD), which were defined in terms of soil thickness, texture, bulk density, organic matter content, erosion modulus and ephemeral gully feature. The results showed that land degradation degree regulated pre-existing soil properties and the suitability of straw return approach. With land degradation degree intensifying, the runoff depth reduction efficiency (RRE) and erosion intensity reduction efficiency (SRE) of SR and SP treatments decreased from 28.5% to 25.8%, 77.0% to 32.3% and 44.5% to 17.9%, 67.4% to 19.3%, respectively. While, RRE and SRE of SM treatment increased from-16.9% to 36.4% and 17.9% to 75.0%. Straw return by rotary tillage was recommended in ND cropland, whereas, straw return by strip mulching was recommended in LD, MD and SD croplands. The main influencing mechanism of straw return to mitigate water erosion in non-degraded cropland was to improve soil structure and promote rainfall infiltration. While, in degraded croplands, the main controlling mechanism was to enhance soil erosion resistance and decline runoff concentration. This study is of great relevance to optimize straw return approach and improve the rational utilization of straw resource in semi humid regions and can help to interpret the mechanism of straw return controlling water erosion under different soil conditions.